1. Field of the Invention
This invention relates to apparatus for collecting soot from the exhaust gases of an air-compressing, self-igniting internal combustion engine, which apparatus comprises a housing incorporated in the exhaust gas line of the engine and arranged to be flowed through by the exhaust gases, baffle walls contained in the housing and arranged to repeatedly deflect the exhaust gas stream, and a collecting container for collecting the seperated soot particles.
2. Description of the Prior Art
In the operation of air-compressing, self-igniting internal combustion engines, i.e., diesel engines operating with direct or indirect fuel injection, the diesel cycle results in a production of exhaust gases which are laden with soot particles of various sizes. Such soot particles are produced mainly during full-load operation of the engine and their emission would pollute the environment and for this reason should be avoided. An improvement in this respect has been achieved by the provision of supercharged engines, which operate with an excess of air so that their soot emission is low. But a removal of soot to a high degree will be particularly important if various measures adopted to reduce the NO.sub.x emission result in a formation of soot at a higher rate. A reduction of the emission of both NO.sub.x and soot can be effected only by special measures, such as the provision of soot filters in the exhaust gas line of the internal combustion engines.
It is already known to provide soot filters consisting of monolithic ceramic bodies in the exhaust gas line of air-compressing, self-igniting internal combustion engines. As the exhaust gas flows through such filters, the soot particles are retained in the fine pores of the filter. But such filter must be regenerated intermittently or continuously because the soot particles retained by the filter must be removed in order to ensure that the filter will remain permeable to the exhaust gas. Otherwise the power of the internal combustion engine would be decreased and its fuel consumption would be increased or the engine might become entirely inoperative. It has been proposed to regenerate the filter in that the soot is burnt either automatically when the filter has been heated to a sufficiently high temperature of about 400.degree. to 800.degree. C. or by the provision of specially arranged burners for heating the filter to the required temperature. These measures involve a high structural expenditure and such regeneration may give rise to difficulties when the filter has been clogged to a relatively high degree and the engine is then operated near its upper load limit to produce exhaust gas at a relatively high temperature because this may result in a sudden burning of the soot in the filter and in a high temperature rise, by which the filter may be entirely destroyed.
It has also been proposed to remove the soot by electrostatic precipitators, in which the soot particles carrying a positive or negative electric charge are collected on electrode plates to which a voltage is applied. By means of an exhaust gas recirculating system the collected soot particles are then returned to the intake side of the internal combustion engine and further to the combustion chambers of the engine. In that case a regeneration of the filter is not required but the recirculated soot particles will increase the wear rate of the internal combustion engine, possibly to a multiple of the wear rate of engines operating without a recirculation of exhaust gases laden with soot particles.
German Patent Publication No. 21 07 745 discloses an exhaust muffler which serves also to purify the exhaust gases of internal combustion engines and comprises a housing that is arranged to be flowed through by the exhaust gases and contains baffle walls for repeatedly deflecting the exhaust gases, and a collecting container for collecting the separated dust particles. In that known muffler the baffle walls consist of partitions in the housing and are rigidly mounted in the housing, and the collecting container is constituted by the lower portion of the housing and is separated from the upper portion of the housing by a horizontal wall, which is perforated like a sieve having holes which decrease in diameter in the direction of flow of the exhaust gases through the housing. That collecting container is not accessible from the outside and cannot be emptied nor exchanged. For this reason that known exhaust muffler will inevitably be clogged in the course of time, particularly if it is used in conjunction with a diesel engine, and will then be inoperative so that it must be replaced by a new muffler. That known exhaust muffler cannot be used at all in trucks for a high mileage.
Published German Application No. 23 36 615 discloses an apparatus which also comprises baffle walls and a collecting container but does not serve to remove soot and other solid particles from the exhaust gases but to effect a condensation in the exhaust gas stream and to recycle the liquid condensate to the intake line of the engine.